1. Field of the Invention
The present invention relates generally to a Diesel cycle internal combustion engine and more specifically to a Diesel cycle internal combustion engine of the type equipped with a swirl chamber which communicates with the main combustion chamber via main and auxiliary transfer ports.
2. Description of the Prior Art
FIGS. 1 and 2 show a prior art arrangement of the type disclosed in Japanese Patent Application Provisional Publication No. Sho 57-179329. In this arrangement a cavity is formed in cylinder head 1. As shown in these Figures the cavity is arranged to have an essentially cylindrical shape, viz., include a right cylindrical face 2A and two essentially flat side walls 2B, 2C. A plug or mouth ring 3 is disposed in the cavity in a manner to close same and define a swirl chamber 4. The plug is formed with main and auxiliary transfer ports 5, 6. The main transfer port 5 is arranged to introduce the charge compressed in the combustion chamber 7 into swirl chamber 4 in a manner that it undergoes a swirling motion as indicated by arrows A.
Fuel injector 8 is arranged to inject fuel into the swirl chamber 4. In this arrangement the injector 8 is arranged to inject fuel along a trajectory which is aimed at the mouth of the auxiliary transfer port 6 so as to cause a fraction of the fuel injected into the swirl chamber 4 to pass through the auxiliary transfer port 6 into the main combustion chamber 7. This distribution of the fuel between the main combustion chamber 7 and the swirl chamber 4 reduces the amount of fuel which undergoes spontaneous combustion in the swirl chamber per se and thus reduces the peak combustion temperature and the amount of NOx formed.
However, this arrangement suffers from the drawback that if the compression ratio of the engine is reduced for the purposes of reducing engine noise or by temporary operation at relatively high altitudes, the reduced amount of gas contained in the swirl chamber 4 at the time when the fuel is injected permits the fuel to penetrate further through the swirl chamber 4 than desirable and actually impinge on the walls of the swirl chamber wetting same particularly around the mouth of the auxiliary transfer port 6. This unsuspended fuel tends to combust more slowly than the portion which is well mixed with air and thus tends to increase the HC and smoke emissions of the engine.
This arrangement further suffers from the drawback that when the above type of swirl chamber is used in combination with a flame dispersing cavity 9 formed in the piston crown (see FIG. 5 by way of example) under the above mentioned conditions wherein the compression ratio of the engine is intentionally lowered for the purposes of reducing engine noise and weight or due to the operation thereof in mountainous areas or the like, an increased amount of fuel tends to find its way through to the elongate trench portion formed between the two essentially circular flame dispersion sections. Accordingly, as this fuel tends to be mixed with an amount of air insufficient to entrain and support complete combustion thereof, further increases in smoke and HC tend to occur.